This invention relates to a dual-mode valvetrain for an internal combustion engine.
Prior art valvetrains include valvetrains that are selectively adjustable to vary the amount of valve travel during opening. Typically, such valvetrains are selectively adjustable between a low-lift mode, in which the valvetrain causes a valve to open a first predetermined amount, and a high-lift mode, in which the valvetrain causes the valve to open a second predetermined amount that is greater than the first predetermined amount. Such dual mode, or xe2x80x9ctwo step,xe2x80x9d valvetrains are significantly larger than comparable valvetrains that are not adjustable, often resulting in incompatibility with existing engine designs without significant modification to the cylinder head design. Furthermore, such prior art valvetrains are complex, with resultant manufacturing and assembly inefficiencies.
A rocker arm assembly for a valvetrain is provided. The rocker arm assembly includes an outer rocker arm characterized by two longitudinally-oriented rail portions spaced a distance apart from one another and defining an open space therebetween. An inner rocker arm is pivotably mounted with respect to the outer rocker arm such that at least a portion of the inner rocker arm is in the open space between the two rail portions of the outer rocker arm. The inner rocker arm has a cam follower thereon for engagement with a low-lift cam, and each of the rail portions of the outer rocker arm has a cam follower thereon for engagement with a high-lift cam.
A locking pin housing on the inner rocker arm has a transversely-oriented locking pin bore formed therein. A first locking pin and a second locking pin are translatable within the bore and selectively movable between an extended position in which they extend into locking pin holes in the outer rocker arm rail portions thereby to prevent relative movement between the inner rocker arm and the outer rocker arm, and a retracted position in which they do not extend into the locking pin holes in the outer rocker arm rail portions.
Thus, the outer rocker arm and the inner rocker arm may move together as a single unit or may move independently of one another within certain constraints, allowing for two discrete valve events on any given inlet or exhaust valve. More specifically, when the inner rocker arm and the outer rocker arm move independently, the inner rocker arm is configured to open and close a valve according to the geometry of a low-lift cam; when the inner rocker arm and the outer rocker arm are locked, the rocker arm assembly is configured to open and close the valve according to the geometry of a high-lift cam. Adjustability of the valve opening allows for engine operating benefits such as improved idle, increased volumetric efficiency, improved combustion performance, reduced fuel consumption due to a variation in the valve timing events caused by the improved combustion performance, and reduced fuel consumption due to a variation in the valve timing events caused by the camshaft which may be controlled by a camshaft phaser, and reduced emissions due to the ability for each of the inlet valves to be lifted differing amounts causing an increase in cylinder air motion. The rocker arm assembly may be employed with both inlet valves and exhaust valves.
The above features and advantages, and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.